1. Field of the Invention
The present invention relates generally to methods and devices for in situ containment of buried waste. More particularly, embodiments of the present invention relate to an improved barrier, as well as to its installation and use, for reliably containing and managing leachate from buried waste.
2. Prior State of the Art
Management and disposal of various types of waste are long-standing problems. Early waste management and disposal systems were primitive, because there were no disposal or environmental regulations in place at the time. In countless instances, the waste was simply buried underground. The volume of waste that has been buried is tremendous. Some experts estimate that landfills in the United States alone hold more than 3 million cubic meters of buried waste. Further, much of the waste that was buried comprises heavy metals such as mercury and cadmium, carcinogenic materials such as trichloroethylene, radioactive materials, and other hazardous substances.
While burial and similar approaches produced an aesthetically pleasing result by removing the waste from sight, it was soon discovered that effluent from the buried waste was working its way through the soil and into the groundwater. This process is commonly known as leaching. Because groundwater is a major source of water for drinking and for agriculture, contamination of the groundwater by leaching is a major concern.
The contamination caused by buried waste is not limited solely to groundwater however. At least some of the groundwater finds its way into waterways such as streams, rivers, and lakes, thus polluting those waterways and poisoning the plant and animal life. Obviously, polluted waterways pose a threat to humans as well, particularly in the case of waterways and bodies of water used for recreational purposes and/or as a source of drinking water.
Not all of the cases of groundwater pollution arise from the leaching of chemicals from waste sources. In some cases, the waste is buried in the path of the groundwater and as groundwater flows through the waste, it collects various chemicals and toxins from the waste, and deposits those chemicals and toxins in other soils and waterways.
Clean soil and groundwater are important to human, plant, and animal life as well as to the environment in general. Accordingly, a variety of methods and devices have been devised to attempt to resolve the problems induced by buried waste. These remedies can be broadly grouped into the categories of remediation and containment. Remediation remedies focus on processes designed to change the chemical composition of a contaminated material or contaminant, while containment remedies seek to eliminate the pollution problem by removing or isolating the contaminants and contaminated material from the surrounding area.
Remediation approaches such as biological treatments, thermal processes and chemical processes are problematic for a variety of reasons. In particular, many of these remediation techniques are expensive and potentially hazardous. Further, it is difficult to verify the effectiveness of many of the treatments and remediation-type approaches may not be appropriate for all types of contaminated material. Finally, determining the proper remediation technique is, in itself, a complex and time-consuming process, particularly in view of the web of regulations and procedures that govern such treatments.
Containment, barrier, or in situ, approaches are problematic as well. One known containment approach is simply to dig up and remove the contaminated soil for treatment and/or disposal. This approach is expensive and time-consuming and often accomplishes little more than moving the problem to another location. Other containment approaches involve installing vertical and/or horizontal barriers around the buried waste. In theory, this approach is attractive because it does not involve digging up or otherwise disturbing the buried waste.
However, these containment or barrier systems suffer from a variety of inadequacies including lack of durability, continuity and integrity. These inadequacies are a function of numerous factors including, but not limited to: exposure to harsh chemicals such as concentrated saline solutions, and saturated calcite and gypsum solutions; exposure to extreme thermal gradients such as are typically experienced in freeze/thaw zones; and exposure to stresses induced by shifting in the earth.
The hydraulic conductivity, which is the rate at which a fluid or hazardous substance flows through a barrier, is unacceptably high in some barrier systems and other typical barrier systems are not particularly well-suited to a variety of soil conditions such as hard rock and sand. A further flaw is that many barrier systems do not provide methods for evaluating the integrity of the barrier during and after installation, which is complicated by the fact that many barrier systems also lack provision for long term monitoring of the containment zone and the leachate therefrom. The inability to monitor a barrier system that is isolating hazardous waste is unacceptable because of the potential harm that can be caused to the environment. The lack of durability, continuity and integrity in known containment systems has a significant effect on the performance of those systems and the effectiveness of those containment and barrier systems cannot be readily determined or evaluated.
Accordingly, what is needed is an improved in situ containment system and a method for installing the system. Specifically, the containment system should be durable so as to maintain both integrity and effectiveness under a variety of physical and thermal conditions as well as adaptable to wide range of soil types and conditions. The containment system should be chemically stable and impervious to attack by the chemicals, compounds, and microbes typically encountered in buried waste. The containment system should also have a low hydraulic conductivity so as to minimize the passage of fluids and chemicals through the barrier and the containment system should monitor the integrity of the barrier both during and after installation. Further, the containment system should be capable of long-term monitoring of the zone enclosed by the containment system and should also be capable of monitoring the leachate from the zone of interest. Also, both the system and the method for installing the containment system should be relatively simple and cost-effective. Finally, the installation method should ensure that the containment system is properly placed and oriented.
The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or completely solved by currently available waste containment systems and methods.
Thus, it is an overall object of one embodiment of the present invention to provide a simple yet cost-effective waste containment system that is particularly useful for in situ monitoring, control, and management of buried waste and associated leachate.
It is another object of one embodiment of the invention to provide a containment system including one or more barriers comprised of interlocking steel casing sections so as to facilitate a durable, impervious and chemically stable containment system having a high degree of continuity and integrity.
A further object of one embodiment of the present invention is to impart added integrity and durability to the barrier by filling the metallic casing sections with an impervious material.
Another object of one embodiment of the present invention is to provide a containment system that employs embedded sensors for long-term monitoring of the integrity of the barriers and for monitoring the containment zone and leachate.
It is also an object of one embodiment of the present invention to provide a containment system installation method that is cost-effective.
Finally, it is an object of one embodiment of the present invention to provide a containment system installation method which will ensure accurate placement and orientation of the containment system.
The effects of buried waste on the environment can be quite profound and are not limited to the area in which the buried waste is located because chemicals, toxins and other hazardous substances associated or produced by the buried waste are frequently introduced into the groundwater and carried to other parts of the environment. These chemicals and other dangerous substances may ultimately be found in drinking water, irrigation water, rivers, lakes, and other sources of water. In this manner, buried waste has an adverse effect on the health of people, plants, and animals and also harms the environment.
In many instances, the buried waste is difficult to move and relocation of the buried waste may actually cause more harm. In these and other instances, it is desirable to contain the buried waste by surrounding the buried waste with a barrier that effectively isolates the buried waste. The containment systems and barriers of the present invention provide an advanced containment system that is continuous, durable, and capable of performing in a variety of geologic and environmental conditions. Additionally, the effectiveness of the advanced containment system is able to be verified over a sustained time period.
In a preferred embodiment, the containment system includes one or more barriers comprising a plurality of metal casing sections longitudinally connected by interlocking structure present on each casing. The barriers cooperate with one or more concrete walls to collectively enclose at least a portion of the buried waste.
Preferably, a barrier is first installed underneath the zone of interest. Specifically, a line of individual steel casing sections are placed by a micro-tunneling device or the like which simultaneously excavates a tunnel and installs connecting casing segments behind the micro-tunneling device as tunneling progresses. The length of the tunnels is determined by the size of the zone of interest to be contained. Preferably, the tunneling device includes a system for ensuring accurate placement and orientation of the tunnels and casing sections. As each tunnel is dug and lined with casing sections, a successive adjacent tunnel is dug and casing sections situated therein which longitudinally interlock with the casing sections placed in the previously excavated tunnel, so as to form a continuous barrier of predetermined width.
The casing sections and the joints whereby they interlock are preferably filled with grout or the like so as to provide an added measure of strength, durability, and imperviousness to the barrier. In a preferred embodiment, two vertical barriers are interlocked with the ends of the horizontal barrier so that the horizontal barrier and vertical barriers collectively form a continuous U or channel-shaped containment boundary around the zone of interest. Preferably, the horizontal and/or vertical barriers include sensors installed contemporaneously so as to permit monitoring of the integrity and performance of the barriers during and after installation. In a preferred embodiment, the barriers also include sensors for long-term monitoring of the zone of interest and associated leachate.
After the channel has been completed, a concrete wall is installed at either end of the containment area, thereby cooperating with the barriers to enclose the containment area on all sides except the top. Optionally, at least one of the barriers has one or more openings in fluid communication with a collection system or the like so that leachate flowing through the opening can be monitored, collected, and processed.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.